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Chapter 5

Pulse Electroplating of Ultrafine Grained Tin Coating

Ashutosh Sharma, Siddhartha Das and Karabi Das

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61255

Abstract

In the electronic packaging industries, soldering materials are essential in joining variousmicroelectronic networks. Solders assure the reliability of joints and protect the micro‐electronic packaging devices. They provide electrical, thermal, and mechanical continuityamong various interconnections in an electronic device. The service performance of allthe electronic appliances depends on high strength and durable soldering materials.Lead-containing solders are in use for years, resulting in an extensive database for the re‐liability of these materials. However, due to toxicity and legislations, lead-free solders arenow being developed. As tin (Sn) is the major component of solders, this chapter presentsthe detailed results and discussion about the metallurgical overview of Sn, synthesis, andcharacterization of pulse electrodeposited pure tin finish from different aqueous solutionbaths. The experiments on pulse electrodeposition such as common tin plating baths em‐ployed, their chemical compositions, rationale behind their selection and their characteri‐zation by bath conductivity and cathodic current efficiency, microstructures, and tinwhisker growth are discussed. Further, the effect of pulse electrodeposition parameterssuch as current density, additive concentration, pH, duty cycle, frequency, temperature,and stirring speed on microstructural characteristics of the coating obtained from sulfatebath and their effect on grain size distribution have been presented.

Keywords: Tin plating, pulse electrodeposition, morphology, plating baths, grain size

1. Introduction

1.1. Background

Lead-bearing solders are in use till date due to their indispensable properties [1–3]. Firstly, itis very cheap, available in abundance and provides good physical and chemical bonding tothe substrate without interfering with the substrate [4–5]. Secondly, lead (Pb) reduces thesurface tension of pure tin, which is 550 mN/m at 232°C, and the lower surface tension of63Sn-37Pb solder (470 mN/m at 280°C) facilitates wetting [4, 6, 7]. The presence of Pb also helps

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,and reproduction in any medium, provided the original work is properly cited.

to prevent the white tin (β-Sn) to gray tin (α-Sn) allotropic phase transformation from occurringin high-Sn solders upon cooling below 13ºC [7]. This makes it a prime choice for soldering.

1.2. Replacement of Pb

There are many technology-based problems that can serve as reasons for the elimination ofSn-Pb solders. First, it has been already proved in the past that many lead-free candidatesolders exhibit significantly better strength and fatigue life properties [4, 6]. Secondly, Pb andPb compounds have been cited by the Environmental Protection Agency (EPA) as one of thetop 17 chemicals posing the greatest threat to human life and the environment [7, 8]. In viewof these reasons, elimination of Pb from electronics is necessary in electronics packaging [1, 6].

1.3. The lead-free definition and regulations

Legislations to restrict the use of Pb were first implemented in the USA in 1991 with the LeadExposure Reduction Act of 1991 and the Lead Exposure Act of 1992, which bans Pb in someapplications and limits Pb content in others to less than 0.1% [7, 8]. In the United States, theNational Electronics Manufacturing Initiative (NEMI) program was developed to research onlead-free alternatives [9]. In Japan, this movement is connected to the Lead-free SolderingResearch Council (1994 to 2000) within the Japan Institute of Electronic Packaging. JapanElectronics and Information Technology Industries Association (JEITA) has set guidelines forlead-free products, which was published in 1999 [10, 11]. These companies aimed to use lead-free solders in mass-produced consumer products and to implement lead-free solderingtechnologies in their products by 2003 [2]. In Europe, the EU directives (WEEE) and (RoHS)have issued a ban on the use of lead in consumer goods [12, 13].

2. Metallurgical overview of Sn

Pure Sn has two allotropes, white tin (β-Sn, metallic) and gray tin (α-Sn, semiconductor). Themost common form of Sn in real life is white tin, which transforms to gray tin at temperaturesbelow 13ºC [14]. β-Sn possesses body-centered tetragonal crystal structure with latticeparameters a = b = 0.5820 nm and c = 0.3175 nm [15]. This c/a ratio of 0.546 gives rise to highlyanisotropic behavior in Sn. The mechanical properties are very poor, the hardness being 11 Hvand tensile strength 44 MPa [16]. This is largely due to its lower melting point relative tocommon engineering metals such as aluminum (Al), copper (Cu), and steel [14–16].

2.1. Pb-free Sn alloys

A relatively large number of Pb-free solder alloys have thus been proposed so far, Sn beingthe primary or major constituent. The two other elements that are major constituents areindium (In) and bismuth (Bi). Other alloying elements are zinc (Zn), silver (Ag), antimo‐ny (Sb), copper (Cu), and magnesium (Mg), and in one case, a minor amount of Pb [1–3].The most popular Pb-free alloy system candidates are listed in a thorough review paper

Electroplating of Nanostructures106

by Abtew and Selvaduray [1]. The most important characteristics that must be consideredin selecting suitable Pb-free solder candidates are: nontoxic; availability; sufficient electri‐cal as well as thermal conductivity; adequate mechanical properties compatible with metallicsubstrates such as Cu, nickel (Ni), Ag, or gold (Au); economically viable; acceptable meltingand processing temperatures; and less temperature effects on substrates, printed circuitboards(PCBs), etc. [1–4, 6].

2.2. Intermetallic compounds and whisker growth

Due to the Pb-free solder implementation, pure Sn and Sn-Cu, Sn-Ag are commonly used toreplace eutectic Sn-Pb as the surface finish on the lead-frames and metal terminations ofpassive devices [17, 18, 19]. However, in Sn-rich lead-free finish, Sn whiskers have been foundto form, which poses a serious threat for the reliability of passive devices. The Sn whiskerformation was first reported in 1946 [20]. It is generally accepted that the driving forces of Snwhiskers mainly attribute to the internal stresses, the dissolution of the metal under-layer, andthe interfacial compound formation. There are two intermetallic compounds of Cu and Snbelow 300ºC, they are Cu6Sn5 and Cu3Sn. The Cu6Sn5 forms at room temperature while Cu3Snforms after annealing at elevated temperatures [21, 22]. Some intermetallic compounds (IMCs),such as AuSn4 for Sn/Au couples, Cu6Sn5 for Sn/Cu couples, and Ni3Sn4 for Sn/Ni couples,even form at room temperature [23, 24].

Based on these three main root-causes of Sn whisker formation, three methods are devised byresearchers to retard the Sn whiskers formation: (1) choosing optimal thickness of the finishlayer, (2) alloying with other metal elements, and (3) adding a reaction barrier layer beneaththe finish layer [25–27].

3. Synthesis routes and technologies for solder fabrication

There are many synthesis routes for the fabrication of solders varying from solid statemechanical alloying, powder metallurgy, sol gel, melting and casting route, chemical routes,gaseous phase sputtering or evaporation methods, electrodeposition method, etc. [28-35].Among all these methods, we will discuss techniques related to thin film pulse electrodepo‐sition of solders. The other methods are not discussed here because they are out of the scopeof this chapter.

3.1. Electrodeposition

Both evaporation and sputter deposition techniques require high vacuum and/or hightemperature processing, which increases operation costs and cause inter-diffusion problems.Compared to these fabrication processes, electrodeposition is an economically viable process[36]. It can be used to plate either single layer or multilayer deposits with easy and precisecontrol of the thickness and composition of each layer. Electrodeposition can be performed onsubstrates with varying sizes and complex shapes and the deposit can be very thin or verythick [37–38]. There are, however, safety and environmental concerns related with chemical

Pulse Electroplating of Ultrafine Grained Tin Coatinghttp://dx.doi.org/10.5772/61255

107

treatment and safe disposal of wastes. Numerous metals and metal alloys have been success‐fully electrodeposited from aqueous solutions. The most useful electrodeposited metalsinclude Sn, Cr, Cu, Ni, Ag, Au, Zn, and alloys such as chromium-nickel (Cr-Ni), iron-cobalt(Fe-Co), and various Sn alloys [36–38].

3.2. General aspects of electrodeposition

In electrodeposition, metal ions present in a solution, the electrolyte, are reduced at the surfaceof an electrode to form a metal layer, as shown in Fig. 1.

Figure 1. A schematic for the electrodeposition process.

This process essentially consists of: (1) an anode (the positive electrode), (2) a cathode (the itemto be electroplated, which is the negative electrode), (3) the electrolyte acts as a transportmedium for the tin ions to be deposited at the cathode as a coating on the item to be electro‐plated, (4) an electric current or voltage source for controlling the deposition, and (5) variousperipherals for contacting the electrodes, stirring and heating the solution, etc. [36–37].

In electrodeposition, the metal is deposited over a conductive substrate by the application ofelectric current through the electrolytic bath. The current provides sufficient energy to proceedthe oxidation-reduction reactions at anode and cathode, respectively. The metal ions in the


electrolyte accept the electrons and get deposited on the substrate. The weight of the depositedmaterial can be calculated from the relation given by Faraday’s laws [37–39]:

Thickness ( )( )time density

J ECE CCE= (1)

where thickness of the deposit is in mg, time in seconds, J = current density, ECE = electro‐chemical equivalent, CCE = current efficiency (ratio of actual/theoretical weight deposited),and density of deposit is in g/cm3.

3.3. Cathodic and anodic reactions

Electrochemical deposition of metals and alloys involves the reduction of metal ions fromaqueous, organic, and fused-salt electrolytes. In this thesis, electrodeposition from aqueoussolutions is being considered. The reduction of metal ions Mn+ in aqueous solution is repre‐sented by [37–39]:

n+ -M + ne M® (2)

Reaction (2) is often accompanied by hydrogen evolution. In acid solutions, we have:

+ -22H + 2e H® (3)

In neutral and basic solutions, hydrogen evolution follows the equation:

- -2 22H O + 2e H + 2OH® (4)

At the anode, the anodic reactions are as follows. In an acidic solution, we have:

+ -2 22H O O + 4H + 4e® (5)

In an alkaline solution, the anode reaction is:

- -2 24OH O +2H O + 4e® (6)

For a soluble anode, oxidation reactions, which will dissolve the anode into solution:

n+ -M M + ne® (7)


109

The equilibrium electrode potential between a metal and a solution of its ions is given by theNernst equation:

/lnn noM M M

RTE E CnF+ +

= + (8)

where Eo is the standard electrode potential, R is the gas constant, F is the Faradaic constant,and CM n+ is the metal ion concentration. It can be noticed that the value of EM /M n+ depends onthe concentration of metal ions to be plated, addition of additives, current density, etc. [38, 39].

3.4. Electrolyte conductivity

The conductivity of an electrolyte depends on the degree of dissociation, the mobility ofindividual ions, temperature (and thus viscosity), and the electrolyte composition. In aqueoussolutions, the ionic conduction depends on the degree of dissociation of dissolved species inthe solution [38, 39]. In order to increase the conductivity of electrolytes, certain salts and acidsor alkali are added; these are known as supporting electrolytes. For acid electrolytes, chloridesand acids are useful; for neutral electrolytes, chlorides are useful; and for alkaline electrolytes,sodium hydroxide or cyanides are useful [39]. Generally, a marked decrease in conductivityat higher concentration is due to the greater coulombic forces acting between the ever closerions in solution. This leads to the loose association of opposite charged ions that are effectivelyneutral and thus no longer contribute to the overall conductivity [39].

3.5. Polarization and overpotential

The equilibrium potential of an electrode differs in an electrochemical cell after the applicationof current. Suppose the equilibrium potential of an electrode when there is no external currentflowing is E. After the application of an external current (I), the potential of the electrode changeby E(I), the overpotential (η) can be given as:

( ) E I – Eh = (9)

It can be also expressed as in terms of current and voltage by the Tafel equation:

a +b log Ih = (10)

where a and b are constants.

The overpotential η is required to overcome hindrance of the overall electrode reaction, whichis usually composed of a sequence of partial reactions, charge transfer, diffusion, chemicalreaction, and crystallization [36, 38]. The overpotential is generally used as a measure of theextent of polarization. Polarization demonstrates departure of the electrode potential from the


equilibrium value upon passage of a Faradaic current [39]. Depending upon the nature andsites of the inhibition factors, there may be different kinds of overpotentials, such as chargetransfer overpotential or activation overpotential, which is caused by inhibition of the chargetransfer taking place across the close proximity of solution/cathode interface.

Thus, four different kinds of overpotential are distinguished and the total overpotential η canbe considered to be composed of four components: where ηct, ηd, ηr, and ηc are, as defined above,charge-transfer, diffusion, reaction, and crystallization overpotentials, respectively. Theelectrode reaction can then be represented by a resistance (RE), composed of a series ofresistances (or more precisely, impedance), which represent the different steps: Rmt, Rct, andRrxn. A fast reaction step is characterized by a small resistance, while a slow reaction step isrepresented by a high resistance. In other words, RE will be the sum of all the resistances Rmt,Rct, and Rrxn, as shown in Fig. 2 [38].

Figure 2. Processes in an electrode reaction represented as resistances (From A.J. Bard, and L.R. Faulkner, Chapter 1:Introduction and Overview of Electrode Processes, Page 24, Electrochemical Methods - Fundamentals and Applica‐tions, 2nd Edition. Reprinted by permission of John Wiley & Sons, Inc. Copyright 2001 © John Wiley & Sons, Inc.

3.6. Pulse current electrodeposition

In olden times, direct current (DC) electrodeposition had only one parameter, namely, currentdensity that is variable. In modern times, pulsed current (PC) plating where the potential orcurrent density alternates rapidly between two different values is used [36–39]. This isaccomplished with a series of pulses of equal amplitude, duration, and polarity, separated bya period of zero current, and time (t) axis as shown in Fig. 3. Each pulse consists of an on-time(Ton), during which potential and current is applied, and an off-time (Toff), during which opencircuit potential and zero current is applied.

The duty cycle is given by the equation:

( )Duty Cycle % onon off

TT T

=+ (11)

The average current density is defined as:

Duty Cycl( e)average peakJ J= ´ (12)


111

Javerage is the average current density and Jpeak is the peak current density [35, 39, 40]. The averagecurrent density in PC plating is similar to the current density used in DC plating. For a givenaverage current density, a number of combinations of different peak current densities and on-off times are available. This gives PC plating two important features. Firstly, a very highinstantaneous current density, one to two orders in magnitude greater than the steady-statelimiting current density as reported, can be used without depleting the metal ions at theelectrode surface [40]. This favors the initiation of the nucleation process and greatly increasesthe number of grains per unit area, resulting in a finer grained deposit with better propertiesthan conventional DC plating. Secondly, during the off-time period, adsorption and desorp‐tion, as well as recrystallization of the deposit occurs, which can control the microstructure ofthe deposits [36, 40, 41].

4. Electrodeposition of Sn

Sn can be electrodeposited from both acidic and alkaline aqueous solutions [42, 43]. In acidicbaths, Sn usually exists as Sn2+ ions, while in alkaline baths, Sn4+ is the more stable species. Thevarious Sn plating baths available in literature are discussed below.

4.1. Sodium stannate baths

The alkaline stannate electrolytes usually contain sodium or potassium stannate and thecorresponding alkali metal hydroxide. These electrolytes are environment friendly, as they arenon-corrosive in nature and do not require other organic additives [42, 43]. The alkaline tinbaths have a very high throwing power and can be operated over a wide current density range.

Figure 3. Schematic diagram of pulsed current waveform.


The tin coatings electroplated from alkaline electrolytes possess improved solderability, sincethey do not require any organic additive agents [44, 45]. This leads to a great improvement inwettability. One major disadvantage of alkaline plating baths is that highly alkaline baths maydissolve the photoresist used to define areas on semiconductor wafers. Alkaline plating bathsalso usually require higher plating temperatures (60–70°C) as compared to acidic ones [46].

4.2. Stannous sulfate baths

Sulfate baths are primarily used for bright acid Sn plating. Organic agents are necessary ifbright and dense films are to be obtained. Electroplating of tin from acidic stannous (divalentSn) solutions consumes less electricity than alkali stannate solutions (tetravalent Sn) [42–45].The major drawback of this system is Sn oxidation. At high current density, soluble Sn anodesare passivated due to the formation of SnO2. Irregular, dendritic, needle-like electrodepositsof tin are in general obtained from acidic electrolytes without organic additives [47–49]. Toimprove the surface finish, morphology, and adhesion during acidic tin plating, variousorganic chemicals as additives have been investigated in the past [50–52]. In the literature, weobserve that sulfate baths have been used widely to plate pure Sn and various Sn alloys inelectronics industries [53].

4.3. Stannous chloride baths

For tin electroplating, sulfate baths use a number of additives to produce a homogeneousdeposit [47–53]. However, in-spite of these advantages, the use of additives is undesirable forhealth concerns. Moreover, adverse effects on plating efficiency and the working environmenthave been observed [54, 55]. In case of alkaline baths, the same is true as it requires heatingthe solution that causes bubble formation [44–46]. Also tin is tetravent in alkaline baths causingmore power. In view of these disadvantages, recently, He et al. developed a bath containingcitric acid or its salt and an ammonium salt [53]. In the same line, Sharma et al. produced bulktin films from stannous chloride-citrate bath and found improved thermal and mechanicalproperties [56].

4.4. Methanesulfonic acid baths

The problem of oxidation of Sn2+ to Sn4+ can be minimized by using a reducing acid Methane‐sulfonic acid (MSA) bath as compared to sulfate bath. MSA is much less corrosive to electronicmaterials than sulfuric acid [55]. It forms a clear solution, have high dissolving power and lesssensitive to Sn oxidation at higher current densities [57]. Different combinations of methane‐sulfonate baths have been developed to electrodeposit both pure Sn and various Sn alloys byadding different additives [58].

4.5. Pyrophosphate baths

There are a number of pyrophosphate baths available in the literature [42]. These types of bathscontaining P2O22- is considered as one of the most stable systems and is widely used for Snplating [59, 60]. However, its use is limited in literature due to one disadvantage, that it requires


113

more control and maintenance than the other plating baths. The operational temperatureshould not exceed 43–60°C because the pyrophosphate complex hydrolyzes to orthophosphateat temperatures higher than 60°C, which degrades the solution [42, 61].

5. Electrodeposition of Sn alloys

According to the electrochemical series of metals, we know that the reduction potential of twoelements would be different [35]. For a solution containing two or more different metal ionsat low overpotential, the metal with the most noble reduction potential will deposit at a fasterrate [35, 36]. If the electrode potential difference is far apart, then metal alloy electrodepositionmay be impossible. The difference can be eliminated in view of the Nernst equation bymodifying the activity values and feasibility of the co-deposition can thus be determined [37,39]. This can be achieved by inducing a considerable change in ionic concentrations viacomplex ion using certain complexing agents. In the past, thiourea has been utilized as acomplexing agent for the electrodeposition of Sn-Ag and Sn-Ag-Cu alloys [62, 63]. Theformation of complexes by bonding the metal ions with complexing agents will decrease theconcentration of the free metal ions in the solution significantly and modify the reductionpotential of the metal ions [64, 65]. With an increase in overpotential, the electrodepositionreaction will progress from the charge transfer region to the mix and then to the mass-transferregime. Under mass transfer control at sufficiently higher overpotentials, the relative deposi‐tion rates of two or more metals will be governed by the concentrations and the diffusioncoefficients of the metal ions [38, 39]. For alloy deposition, the basic mechanism remains thesame as the Sn deposition discussed in the previous section. The summary of the previousstudies on different types of plating baths are given in Table 1.

Coating Processing Methods Plating bath Applications Reference

Sn ElectroplatingSodium stannate bath

+ halidesLead-free Abdel Rahim et.al., 1986 [44]

Sn ElectroplatingSodium stannate bath +

sorbitolSoldering Broggi et al., 2003 [45]

Sn Pulse electroplating Sodium stannate bath Lead-free Sharma et al., 2012 [46]

Sn-Co ElectroplatingStannous sulfate Gluconate

bathLead-free Rehim et al., 1996 [48]

Sn ElectroplatingStannous sulfate bath +

aldehydesSolder joints Tzeng et al., 1996 [49]

Sn Electroplating

Stannous sulfate bath +Benzal acetone and N,N-

bis(tetraoxyethylene)octadecylamine

Lead-free Nakamura et al., 1997 [50]


Coating Processing Methods Plating bath Applications Reference

Sn-Cu, Sn-Bi,and Sn-Ag-Cu

ElectroplatingStannous sulfate bath +

polyoxyethylenelaurylether

Lead-free Fukuda et al., 2003 [51]

Sn-Co Electroplating

Stannous sulfate bath +DS-10 synthanol,

coumarin, formalin (37%solution)

Flip Chiptechnology

Medvedev et al., 2001 [52]

Sn Pulse electroplatingStannous sulfate bath +

triton X 100Solder joints Sharma et al., 2013 [54]

Sn Pulse electroplating Stannous chloride bath Wafer bumps He et al., 2008 [53]

Sn Pulse electroplating Stannous chloride bath Lead-free Sharma et al., 2013 [56]

Sn ElectroplatingMSA bath + PEG, PPG+

PhenolphthaleinSolder bumps Martyak et al., 2004 [57]

Sn ElectroplatingMSA bath + per-

fluorinated cationicsurfactant

Solders Low et al., 2008 [58]

Sn ElectroplatingPyrophosphate bath +

dextrin+ gelatinSolders Vaid et al., 1957 [60]

Sn ElectroplatingPyrophosphate bath +

gelatinLi-ion battery Kim et al., 2010 [59]

Sn-Ag andSn-Ag-Cu

ElectroplatingStannous sulfate bath

+thioureaSolders Ozga et al., 2006 [62]

Sn-Ag-Cu Electroplating

Stannous sulfate bath+thiourea+

polyoxyethylenelaurylether

Lead-free Fukuda et al., 2002 [63]

Sn-Zn ElectroplatingStannous chloride bath +

PEGLead-free Lin et al., 2003 [64]

Ni, Sn, andNi-Sn

ElectroplatingPyrophosphate-glycine

bathLead-free Lacnjevac et al., 2012 [65]

Table 1. Summary of various studies on electrodeposition of Sn.

6. Process parameters and nanostructure formation

The electrodeposition method is dependent on several processing parameters involved in theelectrodeposition process. Therefore, to obtain the desired properties, it is essential to optimize


115

the operating parameters. The effect of these parameters on tin electrodeposition is discussedin the following sections.

6.1. Current density

The current density is the primary controlling parameter in pulse electrodeposition. Theaverage current density Javerage, is given by peak current density Jpeak x Duty Cycle. This enablesus to achieve a very high current density in pulse electrolysis without depleting the metal ionsat the electrode surface [66]. A high overpotential associated with higher pulse current densityraises the nucleation rate resulting in fine grained deposit and thus improved properties canbe obtained [38–40]. For a stable growth, the critical radius of the electrodeposited nucleusvaries inversely to the cathodic overpotential. The higher the cathodic overpotential, the higherthe nucleation rate will be and vice versa [66, 67]. Thus, the grain size decrease with the increasein cathodic overpotential and finer grains are obtained. A higher current density also leads tothe development of dendritic morphology of the deposits [49–54, 56]. The dendritic morphol‐ogy can be suppressed by using additives. For alloy deposition, the change in alloy morphol‐ogy has been noted by several researchers with increase in current densities [64, 65, 68].

The dendritic or irregular shaped morphology in response to the current density is due to thefact that if there is a significant increase in the current density, it increases the nucleation rateand is also associated with a higher rate of hydrogen evolution. Due to high overpotential atthis state, the rate of diffusion of Sn2+ ions towards cathode becomes significant over itsreplenishment from the electrolyte [68, 69]. This phenomenon creates a concentration gradientin the vicinity of electrolyte/cathode interface. As a consequence, the deposition occurspreferentially on certain protrusions (heterogeneous active sites on the cathode in a randommanner. This type of non-uniform growth kinetics has also been observed in copper plating[70]. The cathodic current efficiency at this stage is poor indicating a rapid hydrogen evolutionwhich decreases the concentration of Sn2+ ions in the electrolyte.

6.2. pH

The effect of pH in tin plating has not been discussed in detail in the literature. The majorityof the tin plating baths available in literature are acidic in nature. As a general statement therate of deposition increases with pH [71]. Bath pH not only affects the deposition rate butmodifies the crystal orientation. Some people have noted a pH induced texture in Sn grainsfrom acidic electrolyte [72]. Ebrahimi et al. investigated the effect of pH on nickel deposits [73].He found that the pH values of 4.5, 4.7, and 5.0 resulted in grain size of 79, 45, and 56 nm,respectively. The increasing pH value from 2.8 to 5.1 enhanced the nucleation rate of nickelcrystals, which corresponded to decreasing grain size from 343 to 35 nm. For copper electro‐deposition, Natter and Hempelmann reported the smallest copper grain size of 8 nm at pH1.5–2.0 and a continuous increase of the grain size up to 100 nm at pH 11.5 [74]. The morphologyof the deposited Sn coatings with different bath pH gets refined with an increase in pH. At ahigh value of pH around 2, irregular and porous deposits are observed due to the progressiveincrease in hydrogen evolution reaction. However, at a very high pH (=3), the deposits turnpowdery due to severe hydrogen gas evolution [54].


6.3. Temperature

The majority of acid type formulations operate at room temperature, while alkaline tin bathsneed to be heated at higher optimum temperatures. As the temperature increases, the rate ofdeposition also increases [41, 54, 74]. The velocity (diffusion and migration) of the metal ionsand inhibitor molecules are functions of the temperature. The viscosity of the electrolytedecreases at high temperature, therefore, the diffusion rate and the velocity of metal ions andinhibitor molecules are increased. Sahaym et al. studied the effect of bath temperature in Snelectrodeposits and found the pyramid type morphology at elevated temperatures [75]. Theyvaried the bath temperature from 35ºC to 85ºC and explained that at higher bath/substratetemperature, the cooling rate of the adatoms will be slower. This indicates that at higher platingtemperatures, adatoms can travel to longer diffusion distances on the cathode. This shows thatan increase in the bath temperature may lead to increased grain growth and a smooth coatingsurface. Similar results are shown by Sharma et al. [74]. Bath temperature has been also shownto affect the morphology of the whiskers that formed upon aging at room temperature [75].The metal ions and the inhibiting species have a higher mobility at high temperatures. It resultsin an increase in the concentration of metal ions towards the cathode and a decreases in thecathodic overpotential is observed. This increases the energy barrier (ΔG) for the nucleationprocess according to the equation given by Glasstone in reference [74], resulting in coarsergrain size at higher temperature:

21

'CC

G

h

ì üï ïï ïí ýæ öï ïé ù

+ç ÷ï ïê úë ûè øî þ

D µ (13)

where C ' is the activity of the Sn2+ on the electrode and C is the activity of Sn2+ in the bulksolution. The adsorption rate of inhibiting species decreases at high temperatures due to thedecrease in viscosity causing an enhanced grain growth. It is reported in the past that in anacidic plating bath may decompose at high temperature [41, 42]. Therefore, the plating bathcolor may also change from light to dark yellow and get precipitated. This may be due to thedecomposition of the sulfate entity or oxidation of Sn2+ to Sn4+, which affects the solutionchemistry [41–42, 45, 46]. The plating bath decomposition at elevated temperatures willdecrease the bath conductivity and hence the current efficiency decreases beyond 40°C, witha negligible change in deposit morphology.

6.4. Additives

Although literature review about composite films and nanocrystalline films contains infor‐mation about additives, additives for conventional metal deposition are still important as thoseadditives would provide another aspect of information about deposition mechanism and noveladditives. Popular organic additives that have been used in electrodeposition are gelatin,


117

thiourea, EDTA (Ethylenediaminetetracetic acid), citric acid, benzotriazole (BTA), andinorganic additives such as chloride, are covered in this chapter. Nakamura et al. used variousorganic additives such as benzalacetone (BA) and N, N-bis (tetraoxyethylene) octadecylamine[50]. They found that by increasing the concentration of BA, smaller grains are obtained androughness increases. Further, when both are used with a high concentration of BA, fine-graineddeposits are obtained due to a synergistic action of these adsorbed species. Tzeng et al. studiedthe behavior of aliphatic and aromatic aldehyde groups in tin electrodeposition. They foundthat as compared to formaldehayde and propionoaldehyde, benzaldehyde is hydrophobic innature showing more overpotential and thus acts as the best grain refiner [49]. Surface activeagents such as Triton X-100, aromatic carbonyl compounds, amine-aldehyde reaction prod‐ucts, methane sulphonic acid and its derivatives, etc. [50, 52, 57, 58, 76, 77], are added to platingbaths. The addition of excessive amounts of additives, high current density, and an increasein the concentration of metal ions in the electrolyte may affect the deposit solderability. It ismainly attributed to the oxidation of tin ions in the solution, as well as the aging of the depositin the presence of organic brighteners [76–78]. Fine-grained and smooth deposits wereobtained from acid stannous sulphate solutions containing some aromatic ketones [50]. It wasfound that these organic compounds were adsorbed on the cathode surface and enhanced theoverpotential. In acidic solutions, many other chemicals, such as polyoxyethylene laurylether,triethanolamine, sorbitol, sodium gluconate, 1, 4- hydroxybenzene, Trion X-100, or polypro‐pylene glycol may be added as complexing agents. The additives are necessary to improvesolution stability and deposit morphology. However, an excessive amount of additives wouldmake the coating less solderable [54, 57, 58, 78].

For alkaline stannate bath additives, few reports are available in literature. They usually donot require any additives since deposition occurs at a very negative potential and hydrogenevolution runs parallel with tin deposition acting as a leveler. However, the disadvantage isthe diffusion of hydrogen inside the tin deposits [74–79]. In literature, the effect of additiveshas not been discussed in detail for chlorides electrolytes. Sekar et al. investigated the effect ofadditives in detail on pulse elctrodeposition of tin containing Gelatin, β-naphthol, polyethy‐lene glycol, peptone, and histidine as additives [80]. They observed a grain refinement broughtabout by additives but a marked decrease in current efficiency and found that the bathcontaining peptone has the lowest crystallite size with better corrosion properties. Theselection of organic additive(s) generally depends upon the nature of the metal ions, bath pH,as well as the temperature of the plating solution/substrate. For instance, semi-bright or brightnickel plating solution has different sets of additives as compared to the additives used inacidic zinc plating. Similarly, additives used in acid tin plating baths are different than thoseused in alkaline tin plating. However, the coating morphologies and properties obtained fromacidic and alkaline solutions may or may not be similar to each other. In MSA baths, glycoltype additives, PEG, PPG, and Phenolphthalein have been tried in literature [55]. Glycol-typeadditives are effective in minimizing hydrogen gas evolution at low overpotentials andrefining the grain structure across a wide current density range. These additives are active inthe presence of Phenolphthalein [57]. Low and Walsh used the perfluorinated surfactant inMSA bath and observed that the adsorption of the surfactant hindered hydrogen evolutionand reduced the peak and limiting current densities [58]. There is little information on


pyrophosphate baths in literature. Pyrophosphate baths include mostly glycol additives usedin SnAg type solder bumps. These baths require more control of the electrodepositionparameters. Normally chelating agents and organic additives such as triethanolamine, sodiumgluconate, 1, 4-hydroxybenzene, and Triton X-100 have been added in pyrophosphate baths[42, 59, 60, 61, 81, 82]. The additives are active only up to a certain concentration and have abeneficial effect on the microstructure of the deposits by increasing the cathodic polarization.

At higher concentration of additives, the progressive evolution of hydrogen gas leads to thedevelopment of non-uniform powdery deposits. The powdery deposits generally arise due tothe adsorption and absorption of the hydrogen gases in the deposits according to the followingreactions [54, 83]:

ads 2 2H ---H (14)

+ -adsH + e ----H (15)

ads absH ----H (16)

The additive blocks the association of generated hydrogen atoms according to Equation (14).Consequently, the concentrations of Hads rises following Equation (15). The combined effect ofthese two phenomena (Equations 15 and 16) results in absorption of hydrogen atoms in thedeposits according to Equation (16).

6.5. Duty cycle and frequency

The pulse deposition rate is given by the pulse current density and other parameters such as‘on’ time (Ton) and ‘off’ (Toff) time. The pulse length Ton and Toff time have significant effect ongrain size. An increase in pulse current density at constant length Ton and constant averagecurrent density with an increase in Toff time cause an increase in grain-size, because graingrowth takes place during the Toff time. But an increase in pulsed current density at constantpulse charge and at constant Toff implies a decrease in grain-size. Therefore, a short Ton preventsgrain growth and increases the nucleation rate [32].

The frequency of the pulse is the reciprocal of the total pulse duration consisting of Ton and Toff.The pulse length Ton and Toff time had significant effect on grain size. A higher pulse durationat lower pulse frequencies indicates enough time for the charging (Ton ) and discharging (Toff)of the double layer [36–38]. In contrast, at a high pulse frequency the double layer does not haveenough time for charging and discharging [39, 40]. Thus, lower frequencies cause bigger grainswhile higher frequencies results in a grain refinement of the electrodeposits [36–41, 84].

The deposition rate in the pulse technique is governed by the pulse current density (Jpeak), andon time (Ton) and off time (Toff). At a given peak current density, the duty cycle is given by:


119

( )Duty Cycle % onon off

TT T

=+ (17)

As discussed already, the average current density (Javerage) in a pulse electrodeposition is givenby:

Duty Cycle average peakJ J= ´ (18)

where Jpeak is the peak current density. A 100% duty cycle means there is no pulse used. Theeffect of pulse parameters has been studied in a paper by Sharma et al. [54], where they usedvarious combinations of pulse on and on time to produce several duty cycles as shown in Table2. These combinations are not unique and can be varied according to the desired changes indeposit microstructures.

Duty Cycle (%) Ton (s) Toff (s)

4 0.00042 0.01

10 0.0011 0.01

20 0.0025 0.01

40 0.0067 0.01

60 0.0150 0.01

(Reprinted “With kind permission from Springer Science+Business Media: Journal of Metallurgical and MaterialsTransactions A, Volume 45, 2014, Issue 10, Page 4610-4622, A. Sharma, S. Bhattacharya, S. Das, K. Das, Table II. © TheMinerals, Metals & Materials Society and ASM International 2014”).

Table 2. Pulse parameters at various duty cycles.

However, at a duty cycle of 100%, the grain size observed is usually much coarser. Thus, it isinferred that the grain size of the deposits decreases with an increase in Ton (at constant Toffand Jpeak). An increase in Ton (longer current on times) results in an increased overpotential [84].Youssef and his co-workers have also observed similar behavior in zinc electrodeposits [85].It is reported that the deposit grain size decreases up to a duty cycle of 44%, and an increasein the grain size is noticed beyond duty cycle of 44%. This may be explained due to the factthat the pulse deposition gets transformed to the direct current deposition at this stage [85].

The pulse current (PC) with lower duty cycle (20%) and at direct current (DC) deposition, severe increase porosityis observed. This may be due to higher average current flow time Ton, which triggers hydrogengas evolution [86]. This type of porous deposit morphology can be attributed to the dissolvedhydrogen and oxygen gases in the plating bath. A higher solubility of hydrogen (1617 and 43.3


mg/L in water) compared to that of the oxygen in water (43.3 mg/L), at 25ºC and a 1 bar favorsthe dissolution of hydrogen gas and its incorporation over oxygen in the deposits [86].Therefore, the morphology is rather porous and rough beyond a duty cycle of 20%.

A reduced porosity in case of PC deposition with lower duty cycles can be correlated to thetwo factors. (i) partial diffusion of the hydrogen and oxygen gas away from the substrateduring off time (Toff) and hence a suppressed absorption of hydrogen gas in the deposit; (ii)the total amount of gas generated during the electrolysis of water in on time (Ton) is lesscompared to a continuous DC [54, 86]. Therefore, pulse current with lower duty cycle willresult in a uniform and dense morphology as compared to high duty cycles or DC deposition.

The morphology of electrodeposits is also influenced by the pulse frequency in the electrode‐position. The pulse frequency parameters varied according to Sharma et al. [54] and are shownin Table 3. These combinations are also not unique like the duty cycle and can be varied toobtain the optimum deposit microstructures.

Frequency (f) of the pulse is described as follows:

( )1

on offTf

T=

+ (19)

Frequency 10 Hz 50 Hz 100 Hz 500 Hz

Duty Cycle Ton(s) Toff(s) Ton(s) Toff(s) Ton(s) Toff(s) Ton(s) Toff(s)

10% 0.01 0.09 0.002 0.018 0.001 0.009 .0002 .0018

(Reprinted “With kind permission from Springer Science+Business Media: Journal of Metallurgical and MaterialsTransactions A, Volume 45, 2014, Issue 10, Page 4610-4622, A. Sharma, S. Bhattacharya, S. Das, K. Das, Table III. © TheMinerals, Metals & Materials Society and ASM International 2014”).

Table 3. Pulse frequency parameters

Lower pulse frequency (f) indicates a longer pulse period (Ton+Toff) at a constant duty cycle (D),as shown in Equation (19). The pulse duration is higher at lower frequencies providingsufficient time for the charging and discharging of the double layer.

The Sn atoms can migrate freely to the most stable position facilitating the grain growth. Anincrease in the pulse frequency shortens the pulse duration, i.e., both Ton and Toff are smalleras shown in Table 3. Shanthi et al. have noticed a severe grain refinement during pulse currentplating of silver alloy with short pulse and high frequency [84]. As already discussed, at highpulse frequencies the charging an discharging action of double layer gets poor. These phe‐nomena results in very thin diffusion layers that make the transportation of the migrating Snions towards cathode difficult. The nucleation rate improves as a consequence a densemicrostructure is obtained [85, 66].


121

6.6. Effect of agitation

Agitation in the plating solution can be produced either by agitating the electrolyte or bymoving the cathode. At low agitation rates, the effect of agitation on deposit composition isnot visible, while the agitation rates may decrease the tin content in the coatings. Moreover,agitation may also increase the deposit roughness up to some extent [42, 54]. Agitation hasbeneficial effects of increasing the plating rate and permits the use of higher current densitiesby lowering polarization [36, 37, 38, 39]. Wen and Szpunar studied the nucleation and growthof tin and pointed out that agitation should not exceed beyond a certain limit where turbulentflow occurs that cause the difficulty of tin ions supply to the cathode even at high currentdensities [87]. Thus the cathode coverage is poor and the deposition rate decreases.

It is interesting to note that the stirring rate of the bath has a significant effect on the depositmorphology. The deposition parameters, except the stirring speed that controls the bathagitation, are kept constant. During still deposition, the cathode coverage is poor, and irregularand non-uniform deposits are obtained. This can be explained as when no agitation isprovided, the depositing ions from the electrolyte get deposited preferentially on the cathode.Thus, a concentration gradient is established in the vicinity of electrolyte/cathode interface.The deposition is uneven at this stage and morphology is very poor. When the bath stirring isincreased, the concentration gradient is decreased and deposition rate increases [87, 88].Further stirring of the bath will cause fast transportation of metal ions towards cathode. At asufficiently high stirring rates of the plating bath, the flow of the electrolyte will be turbulentand the metal ions may move away from the cathode vigorously and a lowering in thedeposition rate is observed [88].

7. Sensitivity of the variables and grain size distribution

The electrodeposition parameters considered in this investigation include current density,concentration of the additive, duty cycle, frequency, pH, temperature, and agitation. Theobtained results in this work indicate that the pulsed current electrodeposition can be anefficient method for the electrosynthesis of tin deposits. The surface morphology evolutiondepends on the electrodeposition parameter that tries to modify the overpotential, in a director indirect way. The current density is the most sensitive of all the plating parameters whichaffects the deposit morphology severely. The nucleation rate and grain growth can be signif‐icantly controlled by changing the duty cycle to lower values up 5 to 20%. At higher dutycycles, the porous deposits are produced.

Smaller pulse frequency gives large grained deposits. Thus, a combination of duty cycle andpulse frequency can be optimized for an ultrafine grained or an optimum grain morphologydepending upon the application. The presence of additives in the plating bath improves thesurface finish and morphology if it is added up to its optimum concentration. The currentdensity is found to decrease with bath pH increase. The grain size decreases as pH valueincreases due to the increase in the cathodic polarization. It is also noteworthy point thatpowdery deposits are too developed at very high pH due to the precipitation of stannic


hydroxides. An increase in bath temperature is noticed to raise the grain size of the deposits.However, a decrease in the electrolyte conductivity and current efficiency is noted at elevatedtemperatures due to the precipitation of metal ions in the plating bath. Bath stirring improvesthe availability of metal ions towards cathode and thus the deposition rate is enhanced beforethe flow of electrolyte turns turbulent where the metal ions move away from the cathode. Thegrain size is also increased due to the decrease in overpotential with bath stirring rate

Author details

Ashutosh Sharma1*, Siddhartha Das2 and Karabi Das2

1 Department of Materials Science and Engineering, University of Seoul, Seoul, Korea

2 Department of Metallurgical and Materials Engineering, Indian Institute of TechnologyKharagpur, Kharagpur, India

References

[1] Abtew M, Selvaduray, G. Lead Free Solders in Microelectronics. Materials Scienceand Engineering R. 2000;27:95-141.

[2] Suganuma, K. Lead Free Soldering in Electronics – Science, Technology and Environ‐mental Impact. New York: Marcell Dekker Inc; 2004.

[3] Tu KN, Zeng K. Tin-Lead (SnPb) Solder Reaction in Flip Chip Technology. MaterialsScience and Engineering R. 2001;34:1-58.

[4] Tummala RR. Fundamentals of Microsystems Packaging. McGraw-Hill; 2000. p.185-210.

[5] Liu JP, Guo F, Yan YF, Wang WB, Shi YW. Development of Creep-Resistant, Nano‐sized Ag Particle-Reinforced Sn-Pb Composite Solders. Journal of Electronic Materi‐als. 2004;33(9):958-963.

[6] Sobiech M, Teufel J, Welzel U, Mittemeijer EJ, Hugel W. Stress Relaxation Mecha‐nisms of Sn and SnPb Coatings Electrodeposited on Cu: Avoidance of Whiskering.Journal of Electronic Materials. 2011;40:2300-2313.

[7] Coombs C. Coombs’ Printed Circuits Handbook. USA: McGraw Hill; 2001. p.45.1-45.9.

[8] Subramanian KN. Lead free electronic solders. A special issue of the Journal of Mate‐rials Science: Materials in Electronics. New York: Springer science; 2007. p. 55-76.


123

[9] Suganuma K. Advances in Lead-Free Electronics Soldering. Current Opinion in SolidState and Materials Science. 2001;5:55-64.

[10] Puttlitz KJ, Gaylon GT. Impact of RoHS Directive on High Performance ElectronicSystems. Journal of Materials Science: Materials in electronics. 2007;18: 347-365.

[11] Gilleo K. Area Array Packaging Handbook. New York: McGraw-Hill; 2002.

[12] Puttiltz KJ, Stalter KA. Handbook of Solder Technology for Microelectronic Assem‐blies. New York: Marcell Dekker Inc; 2004. p. 51-55.

[13] Pecht M, Fukuda Y, Rajagopal S. The Impact of Lead-Free Legislation Exemptions onthe Electronics Industry. IEEE Transactions on electronics packaging manufacturing.2004;27:221-232.

[14] Plumbridge WJ. Tin Pest Issues in Lead-Free Electronic Solders. Journal of MaterialsScience: Materials in Electronics. 2007;18:307–318.

[15] Wang Y, Lu KH, Gupta V, Stiborek L, Shirley D, Im J, Ho PS. Effect of Sn Grain Struc‐ture on Electromigration Reliability of Pb-Free Solders. In: Proceedings of ElectronicComponents and Technology Conference; 2011. p. 711-716.

[16] Alam ME, Nai SML, Gupta M. Development of High Strength Sn–Cu Solder UsingCopper Particles at Nanolength Scale. Journal of Alloys and Compounds.2009;476:199-206.

[17] Shen J, Chan YC. Research Advances in Nano-Composite Solders. MicroelectronicsReliability. 2009;49:223-234.

[18] Amagai M. A Study of Nanoparticles in Sn–Ag Based Lead Free Solders. Microelec‐tronics Reliability. 2008;48:1-16.

[19] Chen Z, Shi Y, Xia Z, Yan Y. Properties of Lead-Free Solder SnAgCu Containing Mi‐nute Amounts of Rare Earth. Journal of Electronic materials. 2003;32(4):235-243.

[20] Brusse JA, Ewell GJ, Siplon JP. Tin Whiskers: Attributes And Mitigation. In: Proceed‐ings of 16th Passive Components Symposium (CARTS EUROPE 2002); 2002. p.221-233.

[21] Tu KN. Cu-Sn Interfacial Reactions: Thin-Film Case Versus Bulk Case, MaterialsChemistry and Physics. 1996;46:217-223.

[22] Takenaka T, Kano S, Kajihara M, Kurokawa N, Sakamoto K. Growth Behavior ofCompound Layers in Sn/Cu/Sn Diffusion Couples During Annealing at 433–473K.Materials Science and Engineering. 2005;396:115-123.

[23] Nakahara S, McCoy RJ, Buene L, Vandenberg JM. Room Temperature InterdiffusionStudies of Au/Sn Thin Film Couples. Thin solid films. 1981;84:185-196.

[24] Simic V, Marinkovic Z. Room Temperature Interactions in Copper Metal Thin FilmCouples. Journal of less common metals. 1980;72:133-140.


[25] Tang WM, He A, Liu Q, Ivey DG. Solid State Interfacial Reactions in Electrodeposit‐ed Ni/Sn Couples. International Journal of Minerals, Metallurgy and Materials.2010;17(4):459-463.

[26] Marinkovic Z, Simic V. Room Temperature Interactions in Ni/Metal Thin Film Cou‐ples. Thin solid films. 1982;98:95-100.

[27] Gaylon GT. Annotated Tin Whisker Bibliography. NEMI Tin Whisker ModelingProject; July 2003.

[28] Liangfeng L, Tai Q, Jian Y, Yongbao F. Synthesis of Ag-Cu-Sn Nanocrystalline Alloysas Intermediate Temperature Solder by High Energy Ball Milling. Advanced Materi‐als Research. 2009;79-82:449-452.

[29] Hong Z, Ming TW, Qing XG, Cheng WY, Xiang ZZ. Synthesis of Sn–Ag Binary AlloyPowders by Mechanical Alloying. Materials Chemistry and Physics. 2010;122: 64-68.

[30] Aggarwal AO, Abothu IR, Raj PM, Sacks MD, Tummala RR. Lead-Free Solder FilmsVia Novel Solution Synthesis Routes. IEEE Transactions on Components and Packag‐ing Technologies. 2007;30:486-493.

[31] Hao H, Tian J, Shi YW, Lei YP, Xia ZD. Properties of Sn3.8Ag0.7Cu Solder Alloy withTrace Rare Earth Element Y Additions. Journal of Electronic Materials. 2007; 36 (7):766-774.

[32] Hsiao Li-Yin, Duh Jenq-Gong. Synthesis and Characterization of Lead Free SoldersWith Sn-3.5Ag-xCu (x = 0.2, 0.5, 1.0) Alloy Nanoparticles by the Chemical ReductionMethod. Journal of Electrochemical Society. 2005;159(9):J102-J109.

[33] Conway PP, Fu EKY, Williams K. Precision High Temperature Lead-Free Solder In‐terconnections by Means of High-Energy Droplet Deposition Techniques. CIRP An‐nals–Manufacturing Technology. 2002;51:177-180.

[34] Hsiung CK, Chang CA, Tzeng ZH, Ho CS, Chien FL. Study on Sn-2.3Ag Electroplat‐ed Solder Bump Properties Fabricated by Different Plating and Reflow Conditions.In: Proceedings of 9th Electronics Packaging Technology Conference; 2007. p. 719-724.

[35] Ruythooren W, Attenborough K, Beerten S, Merken P, Fransaer J, Beyne E, Hoof CV,Boeck JD, Celis JP. Electrodeposition for the Synthesis of Microsystems.2000;10:101-107.

[36] Paunovic M, Schlesinger M. Fundamentals of Electrochemical deposition. New Jer‐sey: John wiley and Sons; 2006.

[37] Brown R. RF/Microwave Hybrids Basics. Materials and Processes. Dordrecht: KluwerAcademic Publishers; 2004. p. 169-171.

[38] Bard AJ, Faulkner LR. Electrochemical Methods: Fundamentals and Applications.New York: John Wiley & Sons; 2001.


125

[39] Kanani N. Electroplating: Basic Principles, Processes and Practice. Oxford: ElsevierLtd; 2004.

[40] Chandrasekar MS, Pushpavanam M. Pulse and Pulses Reverse Plating-Conceptual,Advantages and Applications. Electrochimica Acta. 2008;53:3313-3322.

[41] Djokic SS. Modern Aspects of Electrochemistry-Electrodeposition Theory and Prac‐tice. New York: Springer; 2010.

[42] Tan AC. Tin and Solder Plating in the Semiconductor Industry. London: Chapman &.Hall; 1993.

[43] Schlesinger M, Paunovic M. Modern Electroplating. Hoboken, New Jersey: John wi‐ley and sons; 2010.

[44] Abdel Rahim SS, Awad A, El Sayed A. Role of halides in the electroplating of tinfrom the alkaline stannate bath. Surface and coating Technology. 1986;28:139-150.

[45] Broggi RL, Oliviera GMD. Barbosa LL, Pallone EMJA, Carlos IA. Study of an Alka‐line Bath for Tin Deposition in the Presence of Sorbitol and Physical and Morphologi‐cal Characterization of Tin Film. Journal of Applied Electrochemistry.2006;36:403-409.

[46] Sharma A, Bhattacharya S, Sen R, Reddy BSB, Fecht H-J, Das K, Das S. Influence ofCurrent Density on Microstructure of Pulse Electrodeposited Tin Coatings. MaterialsCharacterization. 2012;68:22-32.

[47] Lowenheim F A. Modern Electroplating. New York: John Wiley and Sons; 1974.

[48] Rehim SSAE, Refaey SA, Schwitzgebel G, Taha F, Saleh MB. Electrodeposition of Sn-Co Alloys From Gluconate Baths. Journal of applied electrochemistry.1996;26:413-418.

[49] Tzeng GS, Lin SH, Wang YY, Wan CC. Effect of Additives on the Electrodepositionof Tin From an Acidic Sn(II) Bath. Journal of applied electrochemistry.1996;26:419-423.

[50] Nakamura Y, Kaneko N, Nezu H. Surface Morphology and Crystal Orientation ofElectrodeposited Tin From Acid Stannous Sulphate Solutions Containing VariousAdditives. Journal of applied electrochemistry. 1994;24:569-574.

[51] Fukuda M, Imayoshi K, Matsumoto Y. Effect of Adsorption of Polyoxyethylene Laur‐ylether on Electrodeposition of Pb-free Sn Alloys. Surface and Coatings Technology.2003;169-170:128-131.

[52] Medvedev GI, Makrushin NA. Electrodeposition of Tin From Sulfate ElectrolyteWith Organic Additives. Russian Journal of Applied Chemistry. 2001;74(11):1842-1845.


[53] He A, Liu Q, Ivey DG. Electrodeposition of Tin: A Simple Approach. Journal of Ma‐terials Science: Materials in Electronics. 2008;19:553-562.

[54] Sharma A, Bhattacharya S, Das S, Das K. A Study on the Effect of Pulse Electrodepo‐sition Parameters on the Morphology of Pure Tin Coatings. Metallurgical and Mate‐rials Transactions A. 2013;45A:4610-4622.

[55] Gillman HD, Fernandes B, Wikiel K. Metal Alloy Sulfonic Acid Electroplating Baths.US Patent 6183 619 B1; Feb 6 2001.

[56] Sharma A, Bhattacharya S, Das S, Das K. Influence of current density on surface mor‐phology and properties of pulse plated tin films from citrate electrolyte. Applied Sur‐face Science. 2014;290:373-380.

[57] Martyak NM, Seefeldt R. Additive-Effects During Plating in Acid Tin Methanesulfo‐nate Electrolytes. Electrochimica Acta. 2004;49:4303-4311.

[58] Low CTJ, Walsh FC. The Influence of a Perfluorinated Cationic Surfactant on theElectrodeposition of Tin from a Methanesulfonic Acid Bath. Journal of Electroanalyti‐cal Chemistry. 2008;615:91-102.

[59] Kim RH, Nam DH, Kwon HS. Electrochemical Performance of a Tin ElectrodepositWith a Multi-Layered Structure for Li-ion Batteries. Journal of Power Sources.2010;195:5067-5070.

[60] Vaid J, Char TLR. Tin Plating From the Pyrophosphate Bath. Journal of Electrochemi‐cal society. 1957;104(5):282-287.

[61] Harper CA. Electronic Materials and Processes Handbook. New York: McGraw-Hill;2004.

[62] Ozga P. Electrodeposition of Sn-Ag and Sn-Ag-Cu Alloys From Thiourea AqueousSolutions. Archives of Metallurgy and Materials. 2006;51:413-421.

[63] Fukuda M, Imayoshi K, Matsumoto Y. Effects of Thiourea and PolyoxyethyleneLauryl Ether on Electrodeposition of Sn-Ag-Cu Alloy as a Pb-Free Solder. Journal ofElectrochemical Society. 2002;149:C244-C249.

[64] Lin KL, Sun LM. Electrodeposition of eutectic Sn–Zn alloy by pulse plating. Journalof Materials Research. 2003;18:2203-2207.

[65] Lačnjevac U, Jović BM, Jović VD. Electrodeposition of Ni, Sn and Ni–Sn Alloy Coat‐ings from Pyrophosphate-Glycine Bath. Journal of Electrochemical Society.2012;159(5):D310-D318.

[66] Ibl N. Some Theoretical Aspects of Pulse Electrolysis. Surface Technology.1980;10:81-104.

[67] Watanabe T. Nano-Plating Microstructure Control Theory of Plated Film and DataBase of Plated Film Microstructure. Oxford UK: Elsevier Ltd; 2004.


127

[68] Sharma A, Bhattacharya S, Das S, Das K. Fabrication of Sn-Ag/CeO2 Electro-Compo‐site Solder by Pulse Electrodeposition. Metallurgical and Materials Transactions A.2013;44A:5587-5601.

[69] Liu Z, Zheng M, Hilty RD, West AC. Effect of Morphology and Hydrogen Evolutionon Porosity of Electroplated Cobalt Hard Gold. Journal of Electrochemical Society.2010;157 (7):D411-D416.

[70] Nikolic ND, Popov KI, Pavlovic LJ, Pavlovic MG. Morphologies of Copper DepositsObtained by the Electrodeposition at High Overpotentials. Surface and CoatingsTechnology. 2006;201:560-566.

[71] Durney LJ. Electroplating Engineering Handbook. 4th ed. London: Chapman & Hall;1984.

[72] Teshigawara T, Nakata T, Inoue K, Watanabe T. Microstructure of Pure Tin Electro‐deposited Films, Scripta Materialia. 2001;44:2285-2289.

[73] Ebrahimi F, Bourne GR, Kelly MS, Matthews TE. Mechanical Properties of Nanocrys‐talline Nickel Produced by Electrodeposition. Nanostructured Materials. 2009;11(3):343-350.

[74] Natter H, Hempelmann R. Nanocrystalline Copper by Pulsed Electrodeposition: TheEffects of Organic Additives, Bath Temperature, and pH. Journal of Physical Chemis‐try. 1996;100:19525-19532.

[75] Sahaym U, Miller SL, Norton MG. Effect of Plating Temperature on Sn Surface Mor‐phology. Materials Letters. 2010;64:1547-1550.

[76] Lee JY, Kim JW, Chang BY, Kim HT, Park SM. Effects of Ethoxylated α-Naphtholsul‐fonic Acid on Tin Electroplating at Iron Electrodes. Journal of The ElectrochemicalSociety. 2004;151(5):C333-C341.

[77] Aragon A, Figueroa MG, Gana RE, Zagal JH. Effect of Polyethoxylate Surfactant onthe Electrodeposition of Tin. Journal of Applied Electrochemistry. 1992;22: 558-562.

[78] Lal S, Moyer TD. Role of Intrinsic Stresses in the Phenomena of Tin Whiskers in Elec‐trical Connectors. IEEE Transactions on Electronics Packaging Manufacturing.2005;28:63-74.

[79] Song JY, Yu J, Lee TY. Effects of Reactive Diffusion on Stress Evolution in Cu–SnFilms. Scripta Materialia. 2004;51:167-170.

[80] Sekar R, Eagammai C, Jayakrishnan S. Effect of Additives on Electrodeposition of Tinand its Structural and Corrosion Behaviour. Journal of Applied Electrochemistry.2010;40:49-57.

[81] Neveu B, Lallemand F, Poupon G. Mekhalif Z. Electrodeposition of Pb-free Sn alloysin pulsed current. Applied Surface Science. 2006;252:3561-3573.


[82] Correia AN, Facanha MX, Lima-Neto P. de Cu–Sn Coatings Obtained From Pyro‐phosphate-Based Electrolytes. Surface and Coatings Technology. 2007;201:7216- 7221.

[83] Franklin TC. Some Mechanisms of Action of Additives in Electrodeposition Process‐es. Surface and Coatings Technology. 1987;30:415-428.

[84] Shanthi C, Barathan S, Jaiswal R, Arunachalam RM, Mohan S. The Effect of Pulse Pa‐rameters in Electrodeposition of Silver Alloy. Materials Letters. 2008;62:4519- 4521.

[85] Youssef Kh MS, Koch CC, Fedkiw PS. Influence of Additives and Pulse Electrodepo‐sition Parameters on Production of Nanocrystalline Zinc from Zinc Chloride Electro‐lytes. Journal of Electrochemical Society. 2004;151(2):C103-C111.

[86] Besra L, Uchikoshi T, Suzuki TS, Sakka Y. Application of Constant Current Pulse toSuppress Bubble Incorporation and Control Deposit Morphology During AqueousElectrophoretic Deposition (EPD). Journal of the European Ceramic Society.

[87] 2009;29:1837-1845.

[88] Wen S, Szpunar JA. Nucleation and Growth of Tin on Low Carbon Steel. Electrochi‐mica Acta. 2005;50:2393-2399.

[89] Musa AY, Slaiman QJM, Kadhum AAH, Takriff MS. Effects of Agitation, CurrentDensity and Cyanide Concentration on Cu-Zn Alloy Electroplating. European Jour‐nal of Scientific Research. 2008;22(4):517-524.


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